Micro-mechanical sensor structures may be fragile and may be easily damaged and/or destroyed if they come in contact with foreign particles and/or liquids (including, for example, dirt and condensed humidity). Therefore, it may be desired to protect such structures early in the production process.
Micro-mechanical sensor structures may be protected by applying an additional film of membrane layer during the production process to encapsulate the sensor structure and to shield its sensitive areas from undesired external contaminants, such as, for example, dust and dirt, or potentially harmful environmental conditions, such as, for example heat and humidity. The protective membrane layer, however, may be too thin to withstand the high pressures that may occur during the plastic molding of the micro-mechanical sensor structure device. Although enhancing the thickness of the protective membrane layer may provide greater mechanical stability, such an enhancement may be costly and may not always be feasible, especially if the overall package thickness of the sensor structure device is limited by design constraints.
Micro-mechanical sensor structures may also be protected by stacking several sensor chips or wafers on top of each other within the package. For example, a sensor wafer with etched holes and grooves may be bonded on top of an another sensor wafer to provide reinforcement. In such a configuration, the grooves may be arranged to provide access directly above the sensor structure and the holes may be aligned to provide openings for the contacts. The process of stacking several sensor wafers, however, may increase the material cost (e.g., two wafers may be required instead of only one) and the resulting multi-wafer sensor device may be undesirably thick.